The police mainly.
And we haven't been locked down in NSW for ages although we do have restrictions. For example, our local makes you login to an online register, takes your temperature before you enter, Half the tables are removed and you can't stand at the bar. They put a laminate notice on your table that you turn face down when you arrive and they turn face up again after you have left and the table has been disinfected. Stay for the evening and you will see at least 2 visits by the cops.
In Victoria they were handing fines out like confetti and arrested almost everyone at a small anti-lockdown protest. One man who escaped from a quarantine hotel was given a prison sentence. So we are taking enforcement quite seriously. International and domestic border lockdowns have been a major weapon in that you can almost stop new cases being imported (and where they occur they are already in quarantine) and once you have eliminated within a state you can then keep it that way most of the time and work on getting the other states to zero as well. At the beginning of the Victoria outbreak they had over 700 cases in a day, more or less the same as the UK. They have now not had a case for 21 days. Heroic effort from the people of Victoria imo.